The present invention discloses an aqueous polymerization medium comprising (1) a catalyst composition which contains (a) an organometallic compound and (b) a transition metal compound wherein said catalyst composition is microencapsulated in a polyene product; and (2) water. This invention also discloses an aqueous polymerization medium comprising (1) a catalyst composition which is prepared by dissolving in an inert organic solvent containing at least one polyene (a) a transition metal compound and (b) an organometallic compound and (2) water. This aqueous polymerization medium is very useful in the polymerization of unsaturated hydrocarbon monomers. It is of greatest value in the polymerization of conjugated diolefin monomers into stereo-regulated polymers. This invention reveals a very useful process for producing a polybutadiene composed essentially of syndiotactic 1,2-polybutadiene in an aqueous medium comprising polymerizing 1,3-butadiene in said aqueous medium in the presence of (1) a catalyst component microencapsulated in a polyene product which contains (a) at least one cobalt compound selected from the group consisting of (i) .beta.-diketone complexes of cobalt, (ii) .beta.-keto acid ester complexes of cobalt, (iii) cobalt salts of organic carboxylic acids having 6 to 15 carbon atoms, and (iv) complexes of halogenated cobalt compounds of the formula CoX.sub.n, wherein X represents a halogen atom and n represents 2 or 3, with an organic compound selected from the group consisting of tertiary amine alcohols, tertiary phosphines, ketones and N,N-dialkylamides, and (b) at least one organoaluminum compound of the formula AlR.sub.3 wherein R represents a hydrocarbon radical of 1 to 6 carbon atoms; and (2) carbon disulfide.
The syndiotactic 1,2-polybutadiene produced in accordance with this invention is valuable as the material of films, fibers, and many other shaped products, because of its unique properties such as high melting point, high crystallinity and excellent solvent resistance. Furthermore, this syndiotactic 1,2-polybutadiene exhibits excellent mechanical properties, particularly impact strength, when crystallinity and melting points are moderated.
The polybutadiene produced by the subject process possesses vinyl radical side chains, and consequently shows remarkably improved surface characteristics over those of polyolefin resins. Syndiotactic 1,2-polybutadiene has a unique combination of properties which make it very useful in tires. For example, both wear and rolling resistance are improved by the inclusion of this polymer in tires.
The vinyl radical side chains present in this syndiotactic 1,2-polybutadiene also conveniently allow for the post-treatment of the polymer, such as, crosslinking, graft-polymerization, etc.
Methods for making this polymer by polymerization in hydrocarbons or halogenated hydrocarbon solvents are well-known.
A process for the preparation of 1,2-polybutadiene which comprises polymerizing 1,3-butadiene in the liquid phase, in the presence of a catalyst composition composed of:
(a) a cobalt compound
(b) an organoaluminum compound of the formula EQU AlR.sub.3
in which R is a hydrocarbon radical of 1-6 carbons, and
(c) carbon disulfide is disclosed in U.S. Pat. No. 3,778,424, which is herein incorporated by reference in its entirety. U.S. Pat. No. 3,901,868 reveals a process for producing a butadiene polymer consisting essentially of syndiotactic 1,2-polybutadiene by the successive steps of:
(a) preparing a catalyst component solution by dissolving, in an inert organic solvent containing 1,3-butadiene, a cobalt compound, soluble in the organic solvent, such as (i) cobalt-.beta.-diketone complex, (ii) cobalt-.beta.-keto acid ester complex, (iii) cobalt salt of organic carboxylic acid, and (iv) halogenated cobalt-ligand compound complex, and an organoaluminum compound,
(b) preparing a catalyst composition by mixing the catalyst component solution with an alcohol, ketone or aldehyde compound and carbon disulfide,
(c) providing a polymerization mixture containing desired amounts of 1,3-butadiene, the catalyst composition and an inert organic solvent, and
(d) polymerizing 1,3-butadiene at a temperature of -20.degree. C. to 90.degree. C. This patent is herein incorporated by reference in its entirety.
U.S. Pat. No. 3,778,424 indicates that the presence of water in the catalyst and/or the polymerization system reduces the polymer yield. U.S. Pat. No. 3,901,868 indicates that it is well-known that the organoaluminum catalyst component should be prevented from contact with water.
One aqueous polymerization of a stereo-regulated polymer of commercial significance should be noted. Polychloroprene is made in an aqueous emulsion with a free radical generating catalyst. This polymer has more than 95 percent of its monomer units in a 1,4-configuration (mostly trans). This structural purity is probably caused by steric and electronic effects in the polymerizing chlorinated hydrocarbon monomers, but in any case is quite untypical of a polymer prepared in a free radical polymerization. Some other exceptions to the general rule that stereoregulated polymers can only be prepared in a nonaqueous medium include the preparation of crystalline trans 1,4-polybutadiene which has been synthesized in an aqueous medium employing certain metal salts, such as those of rhodium and ruthenium as the catalyst, and the preparation of trans polyisoprene has also been synthesized in water employing a .pi.-allyl nickel catalyst. 1,2-polybutadiene has been prepared in water using palladium salts as the catalyst. Low yields and other practical problems have discouraged the large scale use of these aqueous polymerizations commercially.
Obviously, the synthesis of stereo-regulated polymers in an aqueous suspension has important advantages over solution polymerization. Water as a medium in which to carry out such a polymerization is less expensive, more easily purified, less sensitive to oxygen, and has a higher heat capacity. Such an aqueous process can be carried out in emulsion-type reactors with little or no reactor modification. The aqueous process also permits higher monomer and higher solids concentrations in the reactor because of the lower viscosity of a polymer suspension compared with a polymer solution.
Unfortunately, it has been the general rule that synthetic stereo regulated polymers can only be synthesized in solution processes. Aqueous processes have not been available in which there was an organometallic catalyst component present.